Treatment of pickle liquor



Dec. 30, i947. J. M. KAHN ETAI.

TREATMENT OF PICKLE LIQUOR Filed March 4, 1945 2 Sheets-Sheet 2v @li uw.

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Patented Dec. 30, 1947 UNITED STATES Ware PATENT YOFFICE TREATMENT OF PICKLE LIQUOR .epplicauon March 4,1943, serial No. 478,034

6 Claims.

This invention relates to a chemical process for treating acid wastes in general, and is a continuation in part of our copending application, Serial No. 457,234, filed September 3, 1942, and which was abandoned January 29, 1945 in favor hereof.

The problem of the disposal of waste acid liquor is sometimes serious. In some cases the quantity to be disposed of may be as much as a million gallons per day or more. The strength of such an acid wasterwill usually vary more or less periodically but it may at times contain as much as 1% of acid or more. Such quantities of acid waste cannot ordinarily be discharged into a stream for Sometimes there is present also some other objectionable impurity as, for instance, iron or other metallic salts in pickle liquor. It has been common practice to run such waste acid liquor over or through beds of broken limestone. Theoretically, this should be effective, but practically it is not in general satisfactory for various reasons, such as the coating of the stone with deposits or coatings of insoluble substances present in the liquid or formed in the reaction. Dosing with fine quicklime or hydrated lime is effective but is expensive and requires treating and control apparatus to get the proper dosing and insure reaction without waste.

The invention further relates to the treatment of waste pickle liquor commonly produced by the steel industry in the acid pickling of steel.

The problem oi disposal of waste pickle liquor is one of the major waste disposal problems of the heavy metal industries. The most common method of disposal has been by ponding, and by discharging of the Waste liquor into rivers, lakes or tide waters whenever possible.V Lime1imestone, or scrap iron can also be used to neutralize the excess acid, the resulting suspension being ponded so that solar evaporation or ground seepage would dissipate the Water. Other methods have endeavored to develop a process whereby usable by-products could be manufactured and recovered, to compensate for the cost of treatment. These processes involve recovery of various iron compounds, the recovery of sulfuric acid, or of ammonium sulfate or gypsum. These processes have a disadvantage of comparatively high cost of installation, equipment, maintenance and operation, due to the corrosive nature of the liquor. Moreover, in many instances, there has been a lack of an adequate market for the byproducts.

An object of this invention, therefore, is to provide a process of treating pickle liquor and other Waste acid liquors which may be operated at a relatively low cost of installation, maintenance and labor.

Another object of the invention is to provide ak process of treating acid liquor in which a marketable by-product is produced which may defray costs of treatment and enable the waste liquor disposal plant to be operated at a net proit; also to improve treating processes for such liquor in other respects hereinafter specified and claimed.

The invention hereinafter described results in the recovery of magnesium hydroxide or oxide, which is readily marketed as a raw material for the production of refractories, or which can be converted to magnesium metal, or which can be used as a basis for the production of othermagnesium compounds. Other products of commercial value may be produced as a result of our process.

This invention in the case of pickle liquor comprises a stage process of cyclic nature. In a simple form the acid liquor is neutralized in a first step with a magnesium compound whereby a solution of a magnesium salt of the acid is obtained, this solution is then treated with dolomitic lime whereby the calcium hydrate or oxide of the lime will precipitate the magnesium of the solution as magnesium hydroxide, commonly called magnesium hydrate, the magnesium hydrate of the dolomitic lime being left in solid form and obtained with the precipitated magnesium hydrate. A suitable part of the so obtained magnesium hydrate is returned to the step wherein the acid is neutralized While the remaining magnesium hydrate is available for any desired use.

Even in this simpler form certain precautions or additional steps may be necessary or desirable. Obviously if the liquid contains suspended impurities that would be objectionable if found in the magnesium hydrate a preliminary treatment such as filtration may be given. Also, if the addition ofthe dolomitic lime would result in the formation of some other precipitate beside magnesium hydrate, suitable measures can easily be taken to overcome this. Thus if the acid to be neutralized is sulphuric acid it may Well be that the amount of calcium sulphate formed upon addition of the lime is beyond the solubility point thereof and in such case we contemplate an additional step wherein the liquid is diluted prior to the precipitation step.

As indicated by subsequent reaction formulae, this treatment may produce approximately double the quantity of magnesium hydroxide used in the initial stage of. the neutralization. In this manner, approximately one-half of the magnesium hydroxide sludge recovered from the last unit can be recycled for subsequent neutralization; and the other portion can be ltered, dried, and calcined as required to produce a marketable magnesium compound. From one aspect our invention may be regarded as a way of securing magnesium oxide from dolomite by reaction with Waste acid liquors that linally leave the magnesium in solid form as hydroxide or oxide While the calcium is retained in solution.

One particularly useful application ot our invention is in the treatment ofv pickle liquor such.

as is produced in the iron or steellindustry.l Since this requires the completestagetreatment that our invention contemplates, we Will for purposes of exemplication now describe our invention in connection with the treatment of such apickle liquor. Furthermore because of its particular applicability in such a process we will, for purposes of illustratiomdescribe our process as carried out in the apparatus sold under the trade name Accel'ator. This apparatus is especially useful in carrying out liquid treatments involving chemical reactions and solids separation. It is to be understood, however, that other forms of apparatus may be used', also that in various cases depending upon the conditions as to character of liquidbeing treated', results sought, etc., the order of steps may sometimes be advantageously altered to some extent or some of the described steps entirely omitted.

The neutralization of pickle liquor with calcium hydroxide or oxide, with the precipitation of iron as ferrous` hydroxide and the formation of calcium sulfate, generally requires a quantity of lime considerably in excess of the stoichiometric amount. When the lime slurry is combined with the pickle liquor, the surfaces of the lime particles are coatedwith-a nearly impervious layer of ferrous hydroxideandsometimes calcium sulfate, thereby decreasing the availability of the lime, necessitating the use of. aconsiderable excess for neutralization. The same difiiculty will be encountered, but to a greater extent, if magnesium` hydroxide were used` for the neutralization, if suitable precaution were nottaken to assure completeness ofreaction. In this case, with the very slight solubility of magnesium hydroxide, the diffusion of hydroxide ion through the interstices of the coated particles would be exceedingly slow, and the eiciency of reactionvery slight. By our process as described, these and otherY dimculties heretofore met With are overcome, and not only are the waste products put in readily disposable form but valuable by-products obtained.

Reference is to be had. to the accompanying drawing forming apart of this specification, in which Figure 1 is a flow diagramlshowing theapparatus and process steps, and

Figure-2 is a central sectional elevation of the Accelatorf Theow diagram incorporates the equipment which is required when thel process involves the precipitation and separation of metallic hydroxides inthe primary and secondary stages of the treatment'. When the process is applied to the treatment of. acids which do not contain metallic salts, the flow diagram canV be simplied as is hereinafter described.

Diiculties previously mentioned are avoided by carrying.' out the'various stages of treatment in units or precipitation apparatus sold under the trade name-Accelator. By diluting the entering pickle liquor with several volumes of the circulating, already treated liquor, as in that apparatus, the tendency for the coating of the magnesium hydroxide particles is decreased, partly due to the precipitation being from a more dilute solution. Also, retention in suspension and circulation of the reaction solids allows a longer time for the reaction and utilizationot the residual magnesium hydroxide.

The first stage of neutralization is carried out in a first or primary Accelator l0 under controlled conditions, after dilution in tank Il if needed, the liquor being treated with a quantity of magnesium hydroxide obtained from magnesium hydroxide precipitation or lnal Accelator l2 and sludge tank I3 Which will react completely with the acid in the pickle liquor. Our tests indicate that a desirable equilibrium is obtained at the pI-I of about 6.0, for which an optimum dosage of magnesium hydroxide can be determined. With a typicalpickle liquor, at this point free acid and the acid of theferric iron will have been neutralized andthe ferrie iron precipitated. The reaction between magnesium hydrate and ferrous iron salt proceeds so slowly that except with quite dilute solutions it is best to interrupt neutralization at this point and complete it later. However, it should be understood that the optimum conditions of neutralization will vary with the composition of the Waste pickleY liquor, as well as with the conditions of treatment. "J

DuringV this partial neutralization, relatively large quantities of iron hydroxide are precipitated. By using the Accelator for thisv treatment, the sludge is concentrated to a minimum volume, andV may be either disposed. of by pending, or may be filtered to recover the magnesium liquor contained and also to recover theiron salts.

In thegure the sludge from primary Accelator ill' is shown to be discharging into sludge tank 3i) from which itis passed to filter 20, the filtrate going toY a secondary neutralization unit or Accelator I4, the residue being disposed of in any suitable manner.

The partially neutralized liquor from primary Accelator l0` and filter 2t! is treated in a second Accelator lliv with calcium hydroxide from lime slaker l5 to raise the pH to a. point which will precipitate the heavy metals completely but not the magnesium. In the. case of a pickle liquor containing ferrous sulfate, it is necessary tovraise the pH to about 8.5 to 9.0, depending upon the conditions. The quantity of lime required for this second stage treatment may result in the production of calcium sulfate in excess of its solubility product. In this case, ferrous hydroxide and calcium sulfate will be obtained-as the Accelator underflow. The clarified neutral liquor, obtained as the overflow, containing magnesium` sulfate equivalent to the amount ofmagnesium hydroxide used in the initial stage of neutralization, will be saturatedA with calcium sulfate. Since the sludge from this stage will contain soluble magnesium salts it is-shoW-n as discharging into sludge tank 3l from which it passes to lter 2|, the residue from which is disposed of. The filtrate is shown as.Y returning to second Accelator I4, but it may goto-the dilution tank, I6; or the third Accelator, l2.

It-` should be understood that this specic applicationdescribes the treatment of a waste pickle A liquor containing ferrous sulfate and sulfuric acid.

esses, as well as salts of the various heavy metals which may be involved. In such cases, it should be understood that the process is equally applicable, although the conditions of treatment may be considerably changed.

The eiuent from second Accelator lil is conveyed into third Accelator l2 for magnesium hydroxide precipitation, either directly or after dilution as in dilution tank l5.

The determining factor of the treatment will be the sulfate concentration of the neutralized acid, as it is necessary to dilute the liquor suiiciently to prevent calcium sulfate from precipitating when the liquor is treated with dolomitic lime in the third, or nal, Accelator l2,

As the waste acids may vary in concentration because of wash or rinse water of lower composition being discharged periodically, our invention contemplates retaining the acid and wash water for a long enough period so that the wash water will dilute the acid to a minimum concentration thereby avoiding calcium sulfate precipitation.

Waste acid may vary considerably in composition. The composition of a typical sample of a pickle liquor produced in one steel plant was as follows:

Per cent FeSO4 5 A typical sample of a pickle liquor from another steel Plant had the following composition:

Although the Accelator is specied as the preferred means for conducting the neutralization, it is understood that these stages of the process could also be carried out in any apparatus which would provide adequate contact of the magnesium hydroxide with the liquor being'treated, and other suitable conditions.

The overflow from the second Accelator lli is diluted in tank i6 to the extent necessary to prevent subsequent precipitation of calcium sulfate. This diluted liquor is treated in the iinal Accelator l2 with slaked dolomitic lime, resulting in the precipitation of magnesium hydroxide, and the concentration of said newly formed magnesium hydroxide as well as the magnesium hydroxide or oxide which is introduced by the dolomitic lime. This reaction can be carried out in any type of neutralizing tank; but it has been found that the recirculation in an Accelator during treatment builds up a magnesium hydroxide sludge of maximum density, and results in complete utilization of the dolomiti@ lime. It has been definitely proven that the precipitation of magnesium hydroxide by such a process results in the production of crystalline magnesium hydroxide which can be dewatered readily by means of rotary vacuum filters, or any other type of filter used for the dewatering of crystalline materials.

The underflow from nal Accelator l2 is shown going in part to sludge tank i3, from which the supply required to effect treatment in rst Accelator l0 is taken, and in part to sludge tank 32. Obviously the sludge tank i3 can be omitted and the rst Accelator l@ supplied with magnesium hydroxide from tank 32. The excess sludge that is available in tank 32, goes to iilter =be washed with treated water from a raw water treating Accelator I9, or other suitable source of wash water, and the filtrate and wash water from the filter Il go to waste.

As noted the liquor from the second or intermediate Accelator l@ is diluted with sufficient water in dilution tank I3 to prevent the precipitation of calcium sulfate in final Accelator l2 when the dolomitic slaked lime is added to the liquor. If this dilution water contains bicarbonates, it is desirably treated with slaked lime from slaker I3 in raw Water treating Accelator I9 so that magnesium hydroxide produced will be pure. While dilution is shown as taking place in a dilution tank I6 for ease of illustration, such a special tank is obviously not necessary in many cases, it being suflicient to join conduits or deliver separate flows into nal Accelator l2.

The reactions involved are as follows:

Primary neutralization (Accelator 10) MgwH)2 H2sol` Mgso4 2R20 Mg(0H)2 resol-nugso4 Femrr)2 (partial precipitation only) BMgwH)2 Fez( sohiaiugso4 2Fe 0H 3 Secondary neutralization (Accelator 14) Ca (OHM FeSO4 CaSO4 Fe(OH)2 (Complete precipitation of ferrous ion) Magnesiumhydroxide precipitation (Accelator 12) MgSOi Ca(OH)2Mg(OH)2- CaSO4 2Mg (OH)2 An Accelator is illustrated in Figure 2 of the drawing. This Accelator consists of a tank 25 having a conical bottom 26 provided with a drain pipe 26a.. A central draft tube 22 is provided with a frusto conical inclined shelf 2l which terminates in a downwardly extending cylinder' 28 which is separated from the bottom 26 by a space 29. An outer draft tube 35 extends around the tube 22 and is separated from the shelf 21 by a space 3l. A rotatably mounted vertical shaft 32 extends axially and vertically through the tube 22 and is provided with propellers 33 and paddles 3d so that slurry contained in the primary mixing and reaction zone 35 below shelf 2l is given a rapid upward movement and overilows the top of tube 22, then flows downwardly in outer draft tube 3d to and through spaces Si and Z9 to be recirculated by the propellers 33.

The raw liquor to be treated passes into zone 35 through a pipe 3l and treating chemical also passes into zone 35 through a pipe 38. The precipitation takes place in the presence of rapidly circulating slurry so that large iiocs are produced which easily settle out. An inclined concentrator partition 39 forms a concentrator chamber 40 and a sludge draw-off pipe il extends into the bottom of chamber iii and is provided with a valve 42 to permit intermittent or continuous removal of sludge from chamber dil. The slurry rises to level 62 in the clarifying chamber 43 and clear liquid rises to the top of chamber 43 to overflow into a launder M formed around the top inside of tank 25 and pass to a point of discharge through a pipe i5. Heavy particles of unreacted lime settle into conical bottom 26 and are withdrawn from time to time through pipe 26a.

In a simple form the cyclic steps of our process may be dispensed with and the magnesium precipitate obtained from the dolomitic lime in a very simple apparatus. Such a simple process may be used when treating a single acid or mixed acids when no metallic salt is present. Where conditions permit, as they occasionally may, all apparatus prior to the treatment tank l2 may be omitted and the acidic liquor, diluted as necessary, may be delivered directly into tank l2 where it is dosed with dolomitic lime. The quan- 7 tit'y: of the lime addedl' should preferably` befisucli. that1the;acid. Will-'reactivith all-oi'the calcium and butv little if' any: ofi the' magnesium, where upon the magnesium oxide anda hydrate? Willi be left. in solid: formi and may be.v removedf through sludge tankzf and'iilt'ered on". or.' otlfiemyisetreati-t edLasidesired. For thistreatmentthe p'H;l oftlie treated liquor is preferably. controlleditoaipoint corresponding to nearly.- butnot.` quite complete neutralization of thelim'e'. ThepI-I-:cf asaturat-`- ed solution.. of. MgOHllz is about. 9.52' and; thatlofr a saturatedV solution of;v Ca(OH);2r about. 1114i. Iii therefore the treatment of.' the :liquor isf controlled by, adjusting the feed' of.r dolomitic' liineto Within this range, thereL will have been. no solution ofi' magnesiumxand there. Wi1l.beno'1.excessl.of unused- (la-(OH) 2. Desirablythe .pI-I ini the. lowfen'dboff the range. In thisway'theaneutralizationiofthe: waste liquor eiects. adirect". separation of." the calcium and magnesium of` the dolomite. It is contemplated that even in this.. simple: form certain other steps may: andfsometim'esf will be required. 'Ilha waste liquor may. requireclariiication beforedosage With-thel dolomite' and may likewise require to be' dilutedlto prevent: preeipitation of impurities. With;t1ie magnesium: In some-leases, as Where the'wasteliquor varies considerably in. acid content. this. dilutionmayy be secured by. anequalizing tank .ofproper'size ahead. of. the. tank i2. in. which` neutralization takes.' place..

As an. example. of. our.. process,.the. following. dataare disclosed:

TREATMENT or. PIcKLr'fLIQUoRz Diluted l to.20.

1st stage-treatment in'zta'nlc'fl 0f 0.088Y lb. Mg OH z per gallon; of" liquor; of`AA` treated liquor 5.8; Mg OHl 2^utilized'l00%...

2nd stage treatment miams-*14:

0.0077 lb. CaOI-Dz perY gallonl or' liquor; pH'of treated liquor 8.4; Tracey of iron left inv liquor4 (less than 0.1 part'per million) Srdsiage treatment-infonie 12 0.2 lb. slaked dolomitic lime per gallon. ofA liquor; Mg OH72 recovered, l'lb. per. gallon.

Inthe claims to follow, the te1rn.pickle liquo will be understood; to.: includa alli Waste liquors.T containing acidzwith orwithouti.a.isalt;ofa: metal; Thus: another Waste: liquori-which may. be; treat;- ed by'our'processf is one containinga-.eopper salt.: and hydrochloric acid..

We would; state in' conclusion: that-,14 While.: the.; illustrated. examples constitute practicalA 'embodili ments of our.` invention, we. doxnotx tlimit; ourselves. precisely to these details; sinceinianir-V festly the same may be considerably varied with,L outdeparting from the spirit of; thefinventionas defined-in the appendedrclaimsi Having-thus described our inventiomvvefclainr as new and; desire `to secure.byr'LettersiPatentti 1. The processor treatingtpicklev liquorcone tainingV freef sulfuric acid, ferricsulfatefand feit rous sulfate, which comprisesmixingzsaid: pickle: liquor Witha-n amount. of an'. aqueoussuspensionz of; magnesium,hydroxide` sufcient to bring: the; pH ofv said pickle liquor to 'approximatelfltand thereby; precipitate ferrie.*hydrloxi'dezandiailirnit;=

8 edamountlof ferrous hydroxide from saidpicklleT liquor,` separating-'the liquid fromsaidprecipitate; and'- adding an. amount of calciumv hydroxide thereto'suiiicient: to f incre ase'. the .pI-Ilof the pickle? liquor to approximately 8';5; andiprecipitateV th'ei balance of iron therefrom.

2i The processes described in. claimV 1f, com prising.: also mixing. the residual magnesiumsul-d fate and calcium sulfate solution formed'by said reactions: 'with' dolomitieilime to precipitate magnesium; hydroxide. the residual solution. beingf kept: sufficiently. dilute to'. prevent precipitation? of'calcium sulfate therefrom.

3: The. process of treatinglwastelpickle liquor? containing ferric sulfate, ferroussulfate andfree sulfuric acid Whichcomprisesestablishing a primary neutralization: zone, a. secondaryV neutral izationazone, and a". magnesium .hydroxide precip=- itation.zone,.maintaining ini each of said-zones: a concentrated slurryfcontaining suspended pari-vA ticles. of like vnaturet'o. those` to be' formedinsaid zone, maintaining a circulationof slurry-in each`v of saidislurry zones', separately introducing Waste pickle liquor andzmagnesium hydroxide into-the primary 'neutralizationzona thereby reacting the. free acid, the ferrie sulfate and a portion ofthe' ferrous'sulfate with the magnesium hydroxide to form a. solution. containingmagnesiumA sulfate'- tion into the circulating slurry in the'magnesium;

hydroxide precipitation zone, addingv dolomitic limeto the solution entering the magnesium hy.'- droxide precipitation zone', thereby precipitating;

magnesium hydroxide'and forming a solutionof."

calcium sulfate, separating,` the solution ofcallciumsulfate from thev precipitated magnesium:v

hydroxide, and returning a portion ofthe mag.-v nesiLun-hydroxide from the magnesium' hydroxide: precipitation zonefinto the primary neutralization.

zone-for treatingy additional quantities of.. pickle.

liquor enteringy said primary neutralization zone'.

4. The process of treating pickle liquor comr tainingiron sulfate',l which comprisesithe steps of: mixing; an amount of magnesium hydroxide with.

said: pickle liquor sufficient to partially neutralize. said pickle liquor and to produce aniron'hydrox'- idev precipitate, separating the precipitater so.4

formed from the liquor; then completely neutralizing:` said liquor with calcium` hydroxide to precipitate the balancevof theV iron as a-lfiydroxide and leave aimixedsoluti'on of'calcium sulfate and magnesium sulfate, diluting. the mixed: solution suciently to prevent subsequent precipitation'of calcium: sulfateY upon'Y treatment with dolomitic.

lime, and'. mixing dolomitic lime with said sulfate solutioirto` precipitatel magnesium hydroxide'andvr leave-a solution of calcium sulfate.

5:1. The cyclic process fory the treatmentfofwaste pickle liquorcontaining-an acid anda ferrici andE a; ferrous salt, which.r comprises mixing anz 7m amount of '.magnesium hydroxide with sa-idliqucr sufcient to neutralize the free acid and precipitate the ferrie iron in the form of ferric hydroxide and form a solution of magnesium salt of the acid, separating said magnesium salt solution from said ferric hydroxide, then completely neutralizing said solution with calcium hydroxide to precipitate the ferrous iron in the form of ferrous hydroxide, thereby forming a mixed solution of calcium sulfate and magnesium sulfate, separating said precipitated ferrous hydroxide from said solution, diluting said solution sufficiently to prevent subsequent precipitation of calcium sulfate when treated with dolomitic lime, adding dolomitic lime to said solution to precipitate magnesium hydroxide, and utilizing a portion of said magnesium hydroxide for the treatment of additional quantities of waste liquor.

6. The cyclic process for the treatment of waste pickle liquor containing free sulfuric acid, ferrie sulfate and ferrous sulfate, which comprises mixing magnesium hydroxide With said liquor to neutralize free acid and precipitate all of the ferrie iron as ferric hydroxide and a minor portion of the ferrous iron as ferrous hydroxide, separating the resulting precipitate from said solution, adding calcium hydroxide to said liquor to precipitate the balance of the iron as ferrous hydroxide, thereby forming a mixed solution of calcium sulfate and magnesium sulfate, the liquor being kept suiciently dilute to prevent precipitation of calcium sulfate therefrom, separating said solution from said ferrous hydroxide, adding dolomitic lime to said solution to precipitate magnesium hydroxide, and utilizing a portion of said magnesium hydroxide for the treatment of additional quantities of Waste liquor.

JAMES M. KAHN.

EDWARD KOMINEK, JR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS OTHER REFERENCES Industrial and Engineering Chemistry, vol. 31,

No. 11, page 1368, Nov. 1939. 

